That is exactly how I had to manage it bangnoise, via an RII patch. I also could not figure out how to send the entire output of Grand VJ into an effect. This *greatly* limits how Syphon can work with it.
You can of course use a Syphon Client as a QTZ “source” to trigger. That works as expected.
In my playing with Grand VJ, it strikes me that they would either have to add Syphon to Grand VJ natively so it grabs the full mixed output, or re-do the effects architecture to make it work in any way that users would reasonably expect a Syphon *output* to work.
Does that clear it up, even if it is somewhat less that helpful? I would petition or ask the Arkaos folks about it.